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Design

UCLA's ST5 fluxgate magnetometer is the product of a long series of successful spaceflight magnetometers. The sensors are boom mounted and have no active components. Drive, sense and feedback signals travel along the boom cable between the sensors and the electronics board on the spacecraft. The electronics whose functional block diagram is shown below generates the fluxgate drive signal, detects the second harmonic of this signal, nulls the field surrounding the sensor, and provides a digital reading of the current needed to null each of the sensors. This signal is then sent to the telemetry system. There is no microprocessor in this simple design. The magnetometer has two commandable ranges, 64,000 and 1000 nT.


The functional block diagram of the UCLA ST5 fluxgate magnetometer showing its drive, sense and feedback circuits.

Sensors

The fluxgate sensors in the UCLA magnetometer are manufactured using the


The 3-axis ring-core fluxgate sensor fabricated by UCLA with a penny in the foreground for comparison.

latest low-noise ring-core technology. UCLA purchased the last of the ring-core material in 1998 and had it fabricated into small (3/8" and 5/8") cores in anticipation of future missions such as ST5. The sensors are similar to our standard design flown on many previous missions. The feedback windings enclose the cores so that in operation the cores themselves are never exposed to strong fields orthogonal to the sense axis that can cause distortions at the level of about 1 part in 104. Thus the sensors are ultralinear and no harmonics of the spin tone will be produced in high fields as have been reported for other missions. The lack of active components on the sensors means that they are very tolerant of temperature extremes. They were qualified at over 100C on Galileo and have operated after being immersed in liquid nitrogen (-196C).

Drive and Sense Circuits

The proposed ST5 magnetometer uses the classic fluxgate circuit presented shown below. Sensor mass and power are kept low with a dual core series drive circuit. The dynamic range is changed from 64,000 nT to 1000 nT by altering the closed loop response from 64,000 nT range to 5000 nT, and then amplifying the signal to get to a 1000 nT range. This method keeps the noise low in both ranges. One gain change command line switches both elements.


Basic fluxgate magnetometer circuit that has been used successfully in space by UCLA for 35 years.

ST5 Magnetometer Design Specifications

Total Mass:       361g + 250g (chassis)
     Electronics Board Mass:       220g
     Chassis:       250g
     Sensor Mass:       75g
     Interface Cable:       < 66g
Electronic Unit Volume:       10x20x5 cm
Sensor Volume:       4x4x6 cm
Interface Cable:       < 100 cm
Power Consumption, Electronics:       500 mW
Power Consumption, Sensor:       50 mW
Range Selection:       1000, 64,000 nT
Data Rate       16 vectors/s
Data Resolution:       18 bits (1:range, 1:sign, 16:value)




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For more information, contact Robert J. Strangeway, strangeway@igpp.ucla.edu.

Last updated June 11, 2001